Session: 10-03: Alternative Energy Conversion Technology (including Wind, Geothermal, Hydro, and Ocean)

Paper Number: 139475

139475 - Techno-Economic Analysis of Low Grade Geothermal Energy Utilization in Southeast Coast Region of China 

Abstract: 

In recent years, the importance of geothermal energy has been on the rise due to its enormous potential, stable heat supply, and minimal environmental impact. However, in most parts of China, the temperature of geothermal reserves is relatively low, making it unsuitable for direct power generation through steam. This limitation, coupled with the low grade of geothermal resources in the region, has hindered the development of geothermal energy in China.

Recognizing the need to widely utilize geothermal energy, it becomes apparent that improving the efficiency of conversion technologies will greatly accelerate the utilization of geothermal heat sources. This, in turn, will help China transition from a fossil fuel-dominated energy source to a more sustainable and renewable one.

In this study, we aim to analyze the techno-economic feasibility of geothermal power generation in China, taking into account geological data and the economic conditions of various cities. We collect and analyze ground heat flow data to inform our analysis. Preliminary findings indicate that the southeast coast region of China offers the most promising potential for investing in geothermal utilization projects, considering both geothermal resource potential and energy demand.

Based on the analysis of resource-demand dynamics, we propose several combined power cycle configurations to facilitate the staged utilization of geothermal energy. Specifically, we focus on examining the feasibility of utilizing geothermal heat sources ranging from 50-150 ℃ for power generation. We introduce a novel combined cycle called the liquefied natural gas, thermoelectric generator, and organic Rankine cycle (LNG-TEG-ORC) combined cycle.

This study improves the overall conversion efficiency and economic indices by incorporating LNG condensation, which enables vacuum condensation to occur at temperatures between -53 to -30 ℃. Additionally, we utilize thermoelectric generators (TEG) to recover cold energy from LNG. To optimize the operating parameters and select the most suitable working fluids, we apply genetic algorithms. The performance of different cycle configurations is compared, and R123 and R245fa are found to be the preferable working fluids for the ORC sub-cycle.

The optimization results reveal that through LNG vacuum condensation and cold energy recovery, the exergy efficiency can be maximized at 23.27%, resulting in a 12.78% increment under a 100 ℃ heat source. Moreover, the levelized cost of energy is estimated to be 23.13 $/MWh, while the specific cost of investment amounts to 0.94 $/W under the same conditions. These findings provide valuable guidance for future geothermal energy utilization and the design of highly efficient combined cycles for geothermal power generation.

Presenting Author: Dongxu Ji The Chinese University of Hong Kong, Shenzhen

Presenting Author Biography: Dr. Ji Dongxu obtained his PhD degree in Nanyang Technological University (NTU). His PhD work is supported by Rolls Royce @NTU Corporate Lab. Starting from 2018, he was employed as Research Fellow in the Energy Research Innovation at NTU (ERI@N), working on energy harvesting and storage. In 2019, he joined CUHK(SZ). Now he works as an assistant professor, working on geothermal energy, solar energy, low grade thermal energy utilization.

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